Wireless Systems Design

Bluetooth Will Answer The Call For CD-Quality Sound

Currently, wireless audio applications are exploding through cell phones and digital music, MP3, and DVD players. This demand is being driven by consumers who are now very used to the CD quality of digital music players. Users realize that they can get music on the Net and enjoy home-theater and many other audio systems with great "surround sound." Now, consumers are taking the next natural step in asking for the convenience of wireless systems. They don't want to be tethered to a headset or speakers to enjoy their music anytime and anywhere. They also want to be able to send their music from one player to another player somewhere else in the house. To fulfill all of these wishes, a good wireless audio link is key.

As stated previously, consumers have grown accustomed to the CD quality of digital audio devices. Naturally, they expect that when they transition to wireless audio devices, they can get the same quality. But in today's environment, this expectation may not be realistic. Implementing CD-quality wireless audio is quite complex. In wireless systems, voice or music is converted to digital signals (packets) and sent over the air. This approach leads to a number of challenges for high-quality wireless audio:

  • During the transmission process, the signal (packets) can be dropped due to absorption by different materials.
  • The signal can suffer from interference from sources like cell or cordless phones and microwave ovens.
  • Audio signals can bounce around and cancel and/or conflict with each other.
  • Echoes and delays may be generated during the data-conversion and transmission process.
  • Different applications require different techniques to protect the audio signals from the hostile environment.

If the system isn't designed correctly, all of these complexities can lead to a negative consumer experience. As a result, consumer wireless audio requires rigorous quality-of-service (QoS) techniques. Such techniques were developed by the advanced cellular and military systems.

High-quality wireless audio also carries the challenge of being a consumer-level technology. It therefore needs to be based on an open standard. Such a standard ensures interoperability among consumer devices and consumer-level prices. Yet it favors the companies that know how to solve the technical challenges of enabling high-quality wireless audio within a standard. Only they will be able to meet the increasingly demanding needs of consumers.

Bluetooth truly is an ideal technology for consumer wireless audio applications. The fundamental core of the technology was invented for military use. The Bluetooth standard made that core into a high-volume, open-standard, consumer-oriented technology. Indeed, hundreds of companies now make Bluetooth devices and products. It is an internationally recognized standard.

It's challenging to apply Bluetooth to high-quality wireless audio applications, however. The basic technology does have the necessary foundation to create the wireless links. Without special care, though, most Bluetooth audio devices will suffer from a number of inadequacies. These faults range from packet loss to crossover and interference, echoes, and generally low quality. To avoid these inadequacies, special techniques are needed to implement Bluetooth for high-quality wireless audio.

Bluetooth has some of the best defenses against interference. It also boasts anti-jamming and low-power requirements. When it's used by experts who know how to leverage its strengths, Bluetooth can achieve excellent, CD-quality audio performance. These parameters help it achieve the QoS that is required by the consumer for wireless audio. Some of the key requirements are explained below:

  1. Jamming margin - A Bluetooth system is fundamentally a spread-spectrum system with high capability against jamming and interference. A wireless system that lacks this capability will generate a lot of "buzzing" noise.
  2. Adaptive frequency hopping (AFH) - To avoid strong interference signals, advanced Bluetooth systems will have AFH technology built in. If AFH is done correctly, it won't interfere with other wireless systems either.
  3. Frequency response - When the system's audio portion is designed correctly, it can achieve the full 20 Hz to 20 kHz bandwidth for the CD quality of the received sound.
  4. Low power - Having low-power design allows the user to enjoy longer hours of listening while moving around.
  5. Audio performance - In order to meet the full CD quality for wireless audio, a system would need to achieve a signal-to-noise ratio (SNR) of 86 dB, an RF sensitivity of −85 dBm, and wide dynamic range.

From the explosive growth in consumer digital audio, a natural path is leading to wireless audio. Bluetooth is ready to answer the call for CD-quality sound. It can serve as the wireless link for many consumer applications. But just plain Bluetooth won't meet the needs of high-quality wireless audio. For such high quality, the basic technology will have to be enhanced in important and specialized ways.

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